Answer
$$\frac{x^4}{15}+10$$
Work Step by Step
Recall, like terms must (1) be raised to the same power and (2) consist of the same variable (i.e. x and y are not like terms). It is also important to note that numbers are all like terms with each other when not multiplied by anything. Doing this, we find:
$$\frac{1}{5}x^4-\frac{2}{15}x^4-2x^2+2x^2+7+3 \\ \frac{x^4}{15}+10$$
